The Diesel cycle is the cycle used in the Diesel (compression-ignition) engine. In this cycle the heat is transferred to the working fluid at constant pressure. The process corresponds to the injection and burning of the fuel in the actual engine. The cycle in an internal combustion engine consists of induction, compression, power and exhaust strokes.

History of? Diesel Cycle

Rudolph Diesel was born in Paris of Bavarian parents in 1858. As a budding mechanical engineer at the Technical University in Munich, he became fascinated by the 2nd law of thermodynamics and the maximum efficiency of a Carnot process and attempted to improve the existing thermal engines of the day on the basis of purely theoretical considerations. His first prototype engine was built in 1893, a year after he applied for his initial patent, but it wasn't until the third prototype was built in 1897 that theory was put into practice with the first 'Diesel' engine.

Design of a Diesel Cycle

The General Idea

The Diesel cycle is very similar to the Otto cycle in that both are closed cycles commonly used to model internal combustion engines. The difference between them is that the Diesel cycle is a compression-ignition cycle instead of a spark-ignition cycle like the Otto cycle. Compression-ignition cycles use fuels that begin combustion when they reach a temperature and pressure that occurs naturally at some point during the cycle and, therefore, do not require a separate energy source (e.g. from a spark plug) to burn. Diesel fuels are mixed so as to combust reliably at the proper thermal state so that Diesel cycle engines run well.
(We might note that most fuels will start combustion on their own at some temperature and pressure. But this is often not intended to occur and can result in the fuel combustion occurring too early in the cycle. For instance, when a gasoline engine - ordinarily an Otto cycle device - is run at overly high compression ratios, it can start "dieseling" where the fuel ignites before the spark is generated. It is often difficult to get such an engine to turn off since the usual method of simply depriving it of a spark may not work.